Systems and methods for an equilibrium wet bath

ABSTRACT

A wet standard calibration system which utilizes a heat conducting foam with the liquid therein to serve as a primary heating device to avoid the need to include mechanical agitation. The system is particularly useful for generating a vapor comprising water and ethanol which can be used for the calibration of breath alcohol testers.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of U.S. Utility patent applicationSer. No. 14/932,637, filed Nov. 4, 2015, which claims the benefit ofU.S. Provisional Application Ser. No. 62/074,975 filed Nov. 4, 2014. Theentire disclosure of both the above documents is herein incorporated byreference.

BACKGROUND 1. Field of the Invention

This disclosure relates to the field of generation of solutes inequilibrium with their vapor phase. These are commonly used as wet bathcalibration systems such as to calibrate breath alcohol testingequipment.

2. Description of the Related Art

For the purposes of public safety on the roads and elsewhere, there is aneed to make sure that individuals are not operating potentiallydangerous machines (such as automobiles) while they are impaired by theeffects of alcohol consumption. To try and prevent people from drivingdrunk, most states have enacted laws that impose fines or other criminalpenalties if individuals have a breath or blood alcohol level above acertain amount. In order to effectively enforce these laws, it isnecessary to be able to measure the alcohol concentration in humanbreath (which is often used as an easy method for approximating bloodalcohol if it is not used directly) and compare the results againstlegal limits. There are a variety of measuring instruments used fordetermining the concentration of alcohol in human breath ranging fromsmall hand held devices to larger bench top units and machines builtinto cars or certain machinery. Since a determination of breath alcoholabove the legal threshold can result in criminal penalties, loss of ajob, or other sanctions, the accuracy of these instruments is paramount.

Great care and effort is taken by owners and managers of evidentialbreath testing equipment to ensure proper calibration as well asfollow-up accuracy checks at generally regular intervals. In attempts toeliminate the labor time of this testing and concerns about human errorin the testing, manufacturers of breath testing equipment often offerautomated or semi-automated methods for doing calibrations and accuracychecks. Some users of breath alcohol test equipment, such as MotorVehicle Law Enforcement, may even require an automatic accuracy checkevery time they test a human subject and sometimes even before and afterthe human subject test simply to make sure that the device is readingcorrectly and will supply court-admissible evidence.

There are generally different standards used when calibrating breathtesters. As breath (containing alcohol or not) is a vapor comprisingexhalation gases and vaporized substances and can be quite complex,instruments that measure alcohol concentration in breath vapor generallyneed standards to be provided in a similar form for accuratecalibration. Calibration gases of many sorts are well known in manyapplications including breath testing. In breath testing, thecalibration standards are generally of two types, wet and dry. Wetstandards include water vapor; dry standards do not. Some argue that wetstandards are better because they include moisture like human breath andare therefore more representative. Effectively, the argument is that thecloser the calibration gas is to the actual constitution of an expectedhuman breath at the tipping point of legal consequences, the more robustthe calibration is, and the more likely that an evidentiary reading willbe determined to be “correct” in the end. However, commercial providersof both wet and dry standards generally advertise +/−2% accuracy ofcalculations with actual breath.

In either case, the alcohol concentration of measurement interest is ina carrier gas such as air, breath, or nitrogen. A typical breath ethanolconcentration which would result in illegal driving in most states is200 parts per million (ppm) or more. That is 200 parts ethanol permillion parts of carrier gas regardless of the carrier gas composition.Therefore, the standards generally provide samples that contain veryclose to 200 ppm to make sure the dividing line is correctly calibrated.

Wet standards have a long history in breath testing, are well accepted,and the liquids used in them can be certified by chemical analysisagainst National Institute of Standards and Technology (NIST) traceablestandards. The standards are prepared by combining known amounts ofethanol and water in a partially filled jar that is accurately heated(generally to 34° C.) and then maintained at that temperature. Theseheated jars are sold commercially and are referred to as Simulators. Atequilibrium, the quiescent headspace above the jar contains a vapor witha known concentration of ethanol along with nearly 100% relativehumidity at that temperature. In one special case of a wet standard,known as an “Equilibrator,” no heating is used, but the operator isrequired to read its temperature (usually equal to ambient) and follow alookup table to see what gas concentration is delivered when similarlyblown through as in a standard simulator.

By introducing sober human breath or air from another suitable sourceinto the jar (by blowing or injecting gas into the liquid), the knownconcentration of ethanol vapor exits the headspace and can be introducedinto a breath tester at which point a measurement may be taken.Typically, a liter or more of gas is blown through the simulator foreach test. As newly introduced air or breath bubbles up through theliquid, it replaces the gas exiting the simulator with newlyequilibrated gas.

Generally, the simulators of the prior art go to great lengths to keepthe temperature of the system constant at 34° C.+/−0.1° C. This isbecause, as the temperature changes, so does the equilibrium point.Thus, the alcohol concentration in the gas varies with the temperatureof the system. For example, at 34° C., a 0.1° change can represent wellover a 0.5% change in the gas. Notably, this air/water equilibriumrelationship for ethanol over temperature is not linear. Those skilledin the art will recognize, as shown in table 1 below that the ratio ofethanol concentration in the air to the water goes up in a non-linearfashion as the temperature goes up:

TABLE 1 ° C. K_(A/W) × 10³ 1 0.035 5 0.046 10 0.073 15 0.107 20 0.155 250.217 30 0.310 35 0.418 37 0.470 40 0.562

Thus, while these types of wet calibration systems are well establishedin the art, there can be no question that there is some concern abouttheir specific ability to provide a highly accurate sample in today'sdemanding environment for repeatable calibration and testing ofmeasurement devices. Prior breath testing devices were commonly alloweda +/−10% accuracy in their readings. As the error introduced from thecalibration sample was relatively small compared to this, it was ofrelatively little concern as most error would exist in the breathtesting device itself. However, today's standards are much more rigorousand most breath testing instruments are allowed, at most, a +/−5% marginof error and are often allowed much less. These specifications can beextraordinarily hard to meet when a calibration standard can, by itself,introduce up to two-thirds of the allowable error. In effect, the breathtesting devices are effectively allowed to have less variation than thestandards they are tested against in order to pass.

While there are some arguments that this simply makes the resultantsystems all the more accurate, it does make clear that even if allprocedures for accurate calibration of the device are followed and thedevice is infinitely accurate, there has always been a degree ofuncertainty in the accuracy of the gas used to calibrate the device.This high degree of uncertainty in the standard has become one of thebiggest components in uncertainty in the instruments and has, in somerespects, resulted in a barrier to the recognition that instruments maybe even more accurate than they currently appear because they simplycannot be accurately calibrated. Thus, there is a need in the art forcalibration systems which reduce their contribution in the uncertaintyof the testing equipment and therefor allow for recognition as to theactual accuracy of the testing equipment itself.

SUMMARY

The following is a summary of the invention, which should provide to thereader a basic understanding of some aspects of the invention. Thissummary is not intended to identify critical elements of the inventionor in any way to delineate the scope of the invention. The sole purposeof this summary is to present in simplified text some aspects of theinvention as a prelude to the more detailed description presented below.

Because of the above and other problems in the art, described herein,among other things, is a wet standard calibration device which utilizesa heat conducting foam with the liquid therein to serve as a primaryheating device to avoid the need to include mechanical agitation.

Described herein, among other things is a wet calibration systemcomprising: a vessel; a thermally conductive foam placed within saidvessel so as to take up a portion of an internal volume of said vessel,a remaining portion of said volume not taken up by said foam comprisinga headspace, said headspace including a gas; a liquid mixture: saidliquid mixture including a solvent and a solute; and said liquid mixturebeing in thermal contact with said thermally conductive foam; and aheating element; wherein, said heating element heats said thermallyconductive foam; wherein said thermally conductive foam heats saidliquid mixture to a temperature; and wherein heating of said liquidmixture generates a vapor in said headspace, said vapor having aconcentration of solute relative to said temperature.

In an embodiment of the wet calibration system, the thermally conductivefoam is a reticulated foam.

In an embodiment of the wet calibration system, the thermally conductivefoam is a metal foam.

In an embodiment of the wet calibration system, the thermally conductivefoam is an aluminum foam.

In an embodiment of the wet calibration system, the thermally conductivefoam is a copper foam.

In an embodiment of the wet calibration system, the liquid is not withinsaid headspace.

In an embodiment of the wet calibration system, the liquid occupies lessvolume in said headspace than said foam occupies in said vessel.

In an embodiment of the wet calibration system, all the liquid is withinone half (½) the distance of the size of an interstitial opening in saidfoam from a surface of said foam.

In an embodiment of the wet calibration system, the solute is ethanoland said solvent is water.

In an embodiment of the wet calibration system, the gas is air.

In an embodiment, the wet calibration system includes an exhaust vent.

In an embodiment of the wet calibration system, the exhaust vent is usedto provide a vapor sample to a breath alcohol tester.

There is also described herein a wet calibration system comprising: avessel; a thermally conductive foam placed within said vessel; a liquidmixture: said liquid mixture including a solvent and a solute having aknown ratio; and said liquid mixture being in thermal contact with saidthermally conductive foam; a heating element configured to heat saidliquid mixture to a known temperature; a gas; and a vapor, said vaporalso comprising said solvent and said solute; wherein, said vapor has aknown concentration of said solute at equilibrium given said knowntemperature and; wherein said liquid and said vapor are in equilibrium.

In an embodiment of the wet calibration system, the thermally conductivefoam is a reticulated foam.

In an embodiment of the wet calibration system, the thermally conductivefoam is a metal foam.

In an embodiment of the wet calibration system, the thermally conductivefoam is an aluminum foam.

In an embodiment of the wet calibration system, the thermally conductivefoam is a copper foam.

There is also described herein a method of generating a vaporcomprising: providing a vessel having a thermally conductive foam placedtherein; placing a liquid mixture of a solvent and a solute in saidvessel so as to at least partially submerge said foam in said liquid;heating said foam to generate a vapor from said liquid, said vapor alsoincluding said solvent and said solute and said vapor and said liquidbeing in equilibrium.

In an embodiment of the method, the thermally conductive foam is a metalfoam.

In an embodiment of the method, the solvent is water and said solute isethanol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a wet calibration device of the prior artthat utilizes a circulating pump for agitation.

FIGS. 2A and 2B respectively show embodiments of a wet calibrationdevice of the prior art that use a mechanical stirrer and a circulatingpump for agitation.

FIG. 3 shows an embodiment of a wet calibration device including a heatconductive foam within the liquid portion.

FIG. 4 provides an embodiment of a wet calibration device including aheat conductive foam that extends from the liquid portion into the gasspace.

FIG. 5 provides an embodiment of a portable wet calibration deviceincluding a heat conductive foam and a vapor permeable membrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Although the present invention will be described hereinafter withparticular reference to the accompanying drawings, it is to beunderstood at the outset that it is contemplated that the presentinvention may be varied in specific detail from that illustrated anddescribed herein while still achieving the desirable characteristics andfeatures of the present invention. Further, while specific embodimentsprimarily designed to calibrate breath alcohol testers are depicted, itshould be understood that components and features can be used across avariety of devices in different types of use. Accordingly, thedescription that follows is intended to be understood as a broadenabling disclosure directed to persons skilled in the applicable arts,and is not to be understood as being restrictive.

With regards to traditional wet calibration systems, such as those shownin FIG. 1, which provides a traditional water bath system (100), FIG.2A, which provides a mechanically stirred water bath (110), and FIG. 2Bwhich provides a circulating water bath (120), the concern is that theconcentration of water and ethanol in the vapor is actually directlydependent on the temperature at the air/water (or more accuratelygas/liquid) interface, and not the temperature in the water as a whole,which is often more conveniently and accurately measured and maintained.The temperature at the interface can be extremely difficult to measureprecisely under ideal conditions and the need to include some form ofmechanical agitation to make the liquid a more homogenous temperaturecan also result in this exact interface temperature being even moredifficult to measure and, often more importantly, to maintain.

FIGS. 3, 4, and 5 provide for three embodiments of a wet calibrationsystem which uses a heat conducting foam (209) in order to heat theliquid (203). The system (200) generally comprises a closed vessel (201)interior within which liquid (203) and vapor (205) can be held at aconstant temperature. The vessel (201) may include a valve mechanism(207) or other structure to allow for vapor (205) from the system (200)to be dispensed to a device to be tested or calibrated and/or forpressure release. The valve mechanism (207) can also or alternativelyact as a septum where an inlet from a gas analyzer (e.g. a breath straw,tube, or probe) can be inserted into the gas space for extraction of asample into the analyzer. Alternatively, the vessel (201) may bedesigned to have necessary components of a device to be tested enclosedwithin itself to allow for a sealed environment.

It should be recognized herein that this disclosure will generally referto the system (200) including a vapor (205) and a liquid (203). Itshould be recognized that these terms are used because, in desiredequilibrium, some of the liquid (203) will generally be suspended in agas (205) present in the system (200). In an embodiment for calibrationof breath alcohol testing equipment, the liquid (203) will generallycomprise a liquid solvent (generally water but that is not required)with a liquid solute (generally ethanol but that is not required)therein. The vapor (205) will generally comprise air (or a gas ofroughly similar composition to air although that is not required) withvaporized liquid solute and solvent therein. However, the composition ofthe liquid (203) and vapor (205) used herein are not necessary andvirtually any liquids, gases, or vapors can be included depending on thedesired equilibrium state and the purpose to which the system (200) isto be put.

Because of the flexibility of terminology, it should be recognized thatreferences herein to a “gas” may refer to a carrier gas (e.g. air) ormay refer to the carrier gas and liquid vapor solution and may be usedinterchangeably with “vapor.” Further, “liquid” may refer to a solvent,solute, or both in combination. Also a “fluid” will generally refer tothe liquid, but may be used to refer to material in either the liquid orgas state and will often be used to indicate that material in eitherstate is being indicated.

Heat is provided to the liquid (203) via a conducting reticulated foam(209), generally a metal foam, as the primary heating element. In anembodiment, the liquid (203) generally completely fills all theinterstitial openings of the foam (209), keeping all portions of theliquid (203) in close contact with the foam (209) and at constanttemperature. In such an embodiment, the liquid level (213) (and thus theline of liquid/gas interface (213)) will generally be very close to theheight of the foam (209) so that the gas/liquid interface (213) is at ornear the uppermost surface of the foam (209). In an embodiment, theinterface (213) may begin just slightly above the foam (209) so as toprovide an actual planar interface (213) between vapor (205) and liquid(203). In an alternative embodiment, the interface (213) level may beslightly below the upper surface of the foam (209) so as to provide forgas (205) heating as contemplated below in conjunction with FIG. 4.

The various interstitial openings (219) within the foam (209) arepreferably fully interconnected (allowing liquid (203) at any point inthe foam (209) to potentially flow to any other point in the foam (209))and open to the outside of the foam (209) (e.g. an opening (219) wouldcontact a wall of the vessel (201) so that liquid (203) could exit thefoam (209) depending on the space between the wall of the vessel (201)and the outside of the foam (209)). However, this is not necessary inall embodiments. The interconnection, however, allows fluids to passfreely into and out of the foam (209) structure and inhibit the creationof heated “pockets” which cannot readily transfer heat.

The foam (209) may be of any type that is capable of being heated or ofgenerating heat and transferring that heat to the liquid (203).Typically the foam (209) will be a metal foam and is preferably amaterial which does not react with water or ethanol. This can include,for example, copper, aluminum, silver, or gold One example of a useablereticulated foam (209) is Duocell® from ERG Aerospace Corporation. Thefoam (209) will generally be designed to be heat conductive even if itis non-metallic.

As shown in FIG. 3, the liquid (203) in the vessel (201) does notrequire circulation for precise temperature control as virtually all theliquid (203) is in very close proximity to the material of the foam(209) as it is within the channels (219) of the foam (209). In anembodiment, if the foam is manufactured with a generally consistentopening (219) size, the liquid will have a maximum distance from thefoam of one-half (½) the opening size. Further, this distance can thenalso be used to dictate the preferred depth of liquid (203) above theupper surface of the foam (109). As the foam (209) transfers heat to theliquid (203), the liquid (203) will be efficiently heated by itsproximity at a general regular rate.

Further, to the extent there are small temperature variations (which arebelieved to be slight due to the close proximity), temperature inducedcurrents will generally cause warmer and cooler liquid (203) to beintermixed quickly and efficiently throughout the foam (209). Thus,temperature in all the liquid (203) which is within the foam (209)should be maintained at a very constant temperature without the use ofor need for mechanical agitation.

Because the liquid (203) bath is not being mechanically agitated ormechanically circulated, the liquid (203) and liquid/vapor interface(213) represent a simpler system of temperature control while providinga liquid (203) bath with an essentially homogeneous or near homogenoustemperature. The temperature of the liquid/gas interface (213) can,therefore, be more precisely controlled. Specifically, the temperatureof any part of the liquid (203) will generally be very close to anyother part and, to the extent they are different, they should rapidlyconverge by simple heat transfer and convection currents. Thus, theentirety of the liquid (203) is generally at a fairly constant andcontrolled temperature. Such consistency, means that the temperature ofthe liquid (203) at the liquid/gas interface (213) is also generallyvery close the temperature of all the other liquid (203) and sinceagitation and movement of the liquid (203) at the liquid/gas interface(213) is relatively minimal, its temperature is highly controllable.

While not required, it is preferred that the vessel (201) be thermallyconductive to better facilitate the transfer of heat from a heater (211)which can be mounted outside the vessel (201) to the reticulated foam(209). Good thermal connectivity may be achieved by press fitting theoutside shape of the foam (209) into the vessel (201), which ispreferably also made of metal or other conducting material, so that thefoam (209) is forced to have many good thermal contacts with andthroughout the enclosure and by using an enclosure with a large amountof thermal conductivity. Heating elements (211) also can be distributedaround the outside of the container to heat from a variety of differentpositions simultaneously. Regardless of the types of heating elements(211) used, it is generally preferred that the system (200) be capableof being heated and maintained at a specific temperature above ambientfor a long period of time to further promote a consistent temperature.External heating, however, is not required and in an alternativeembodiment the heating element (211) may be mounted interior to thevessel (201) or the foam (209) itself may convert another form of input(for example, an electrical signal) into heat directly to heat theliquid (203).

It is generally preferred that in order to monitor and maintain thetemperature inside the vessel (201) that there be provided a thermometer(221) arranged to detect the temperature inside the vessel (201). Thethermometer (221) also may be conductive, and may obtain the temperaturefrom the exterior surface of the vessel (201). However, the thermometer(221) may operate best if it is within the vessel (200). As such, it maybe positioned in the liquid (203), in the vapor (205), or at thegas/liquid interface (213). It is generally believed that more accuratetemperature control can be achieved if the thermometer (221) is incontact with the liquid (203) only and is positioned within a well deepinside the foam (209) but at a point where liquid (203) is capable offlowing to the other points in the foam (209) and particularly to theliquid/gas interface (213). In this way, the thermometer (221) ismeasuring the temperature of the liquid at a point where thermalcurrents should have reached an equilibrium. In alternative embodiments,the thermometer may be in contact with the foam (209), gas (205), and/orinterface (213) as well as the liquid (203).

The thermometer (221) can be any of a variety of temperature sensorssuch as thermistors or thermocouples. Generally, the type of thermometer(221) will depend on the exact nature of an associated control system(231). The control system (231) would serve to interconnect the outputof the thermometer (221) to control of the heater (211) such that whenthe thermometer (221) is to detect a change in temperature, the outputof the heater (211) would be automatically adjusted to compensate in afeedback loop type of arrangement. Such arrangements are well known tothose of ordinary skill in the art and therefore not discussed in detailhere. To improve control, the thermometer (221) will generally belocated in a position that delivers the best indication that the fluidin the vessel (200) has reached equilibrium (e.g. it may be at a pointwhere equilibrium takes longer to obtain) and be calibrated so that thetemperature detected can be readily converted into the temperature atthe gas/liquid interface (213) that is desired.

Because the vessel (201) is designed generally to be sealed, and may beoperating for a period of time without being used for any testing ofexternal devices (which would necessarily vent some vapor), the gasspace (205) may include one or more venting valves (which may be themeasurement valve (207) or another valve) to maintain pressure insidethe vessel (201) in equilibrium with ambient pressure and inhibit anypotential danger to the vessel (201) from a severe over or underpressure. Further, use of valves to maintain pressure will also assistin maintaining the temperature internal to the vessel (201) as thetemperature will not be affected by changes in pressure as it internallyheats or cools. The system may also include a liquid input which canserver to add additional liquid (203) to the vessel (201) as the amountdecreases. This can provide that the liquid (203) level does not getbelow a certain desired level to also assist in maintaining equilibrium.

It should be recognized that while the above description contemplatesthe foam (209) being used to heat the liquid (203) above ambient, thisis by no means required. In an embodiment, the foam (209) with attachedheater (211) may be used to heat the liquid (203) above ambienttemperature, or the foam (209) may be used to cool the liquid (203)below ambient temperature by use of a connected thermoelectric elementbased on the Peltier effect, for example. The system (200) also can beused without the heater (211) as contemplated later herein.

FIG. 4 provides for an alternative embodiment of the system (200) wherethe reticulated foam (209) has a portion (239) which extends into thegas (205) space. As shown in FIG. 4, the extension (239) will generallynot pass through the entire plane of the liquid/gas interface (213), butwill instead only extend at a sub-portion. However, in an alternativeembodiment, the foam (209) may extend at all points placing the plane ofinterface (213) within the foam (209). An embodiment with the foam (209)extending into the gas space (205) can provide for additionaltemperature control of the entire system (200). Specifically, as theportion of the foam (239) in the gas space (205) is filled with gas(205) and is contiguous with the foam (209) in the liquid space (203),this creates a continuous heat exchanger across the interface (213), aportion of which heats the liquid (203) and a portion of which heats thegas (205). Like the liquid (203), the gas (205) can pass freely into andout of the foam structure (239). However, the heat can now exchangedirectly with either the liquid (203) and/or the gas (205) from the foam(239) or (209). This can provide for a better fluid flow within thevessel (201).

As is shown in FIG. 5, a vapor permeable membrane (243) may be used tokeep liquid (203) from ever entering the gas space (205). While in mostcases such interaction is not a problem so long as it is minimal (e.g.in the form of a popping bubble), prevention of the interaction can beimportant in a device (200) where orientation cannot be controlled atall times. For example, if the device (200) is used in a portableapplication, the device (200) may be positioned on a surface which maynot be level. This could cause the upper most foam surface (229) tocross the liquid/gas threshold (213) at an angle and in a manner thatmay not allow for accurate heating. Similarly, as seen in FIG. 5, partor all of the system (200) also may be thermally insulated (241) forbetter temperature control of the entire system (200) or parts thereofwhere such insulation (241) is desired.

While the system will generally be used to provide for the ability tospecify and hold a particular temperature in the liquid (203) (and atthe gas/liquid interface (213)) so as to provide for a consistent,repeatable, steady state inside the chamber (200) without the need formechanical agitation, it should be recognized that the system (200) canprovide for a variety of potential uses and operations within thatrealm.

In the first instance, the system (200) can be used to create a knownvapor (205) mixture with a high degree of accuracy. With a partitionrelationship between a solute in a liquid phase (203) (in a solvent) andsaid solute in a gaseous phase (205) (in equilibrium above the liquid)known at a given temperature, by mixing the solute in some exactconcentration of solvent (which is relatively easy), and placing theproper amount of such liquid mix (203) in the vessel (201), a vapor(205) of predictable concentration is created in the headspace above.Such vapor (205) can be used for any variety of purposes includingcalibration of gas analysis equipment or in producing vapors (205) ofknown concentration to have certain effects (e.g. for vapor etching,theatrical vapor effects, or for precise steam cooking). By varying theliquid (203) concentration at will, proportional concentrations of gasmay be created at will.

It should be recognized in the above, that while making a specific vapor(205) from a specific liquid (203) by having a fixed temperature isgenerally contemplated, it is generally the case that temperaturevariation can be used to create different concentrations from the samesource liquid (203). Thus, with a single liquid (203) mix of knownconcentration of solute in solvent, the temperature of the liquid (203)can be controlled at will, with precision, to create an accordinglyproportional and predictable vapor (205) concentration. This can be usedfor variations of the vapor (205) concentration over time, or to allowthe device (200) to provide a wide variety of vapor (205) concentrationsdepending on application.

Further, while the above generally presumes that the temperature iscontrolled by the device (200), in some cases the device (200) canactually be used to predict potential errors produced by ambientconditions. For example, in the event that the device (200) is beingused in an unknown environment, the heater (211) can be turned off andthe system (200) can be used to measure the temperature at ambient. Fromthis, and knowledge of the concentration of the liquid (203) mix, thesystem (200) can determine the vapor (205) concentration at ambient.Within some reasonable ambient temperature range, the range of vapor(205) concentrations produced may still be within a reasonable enoughrange to calibrate or check gas analysis equipment, even though the usermust use the vapor (205) concentration predicted by the ambienttemperature and the system (200) instead of being able to always counton a specific concentration. Thus, even though the exact concentrationof the vapor (205) is not under absolute control of the user, it isstill a precise enough value to use. Further, because the system (200)can create a known calibration vapor (205) at ambient temperature, aremote device can be correctly calibrated at ambient. In this way, adevice being calibrated where the reaction for measurement istemperature dependent (e.g. not the same across all temperatures) can becalculated at its current ambient temperature, resulting in the mostaccurate calibration possible.

Still further, the device (200) also can be used to evaluate a liquid(203) mix of unknown concentration of a known solute. Specifically, byplacing the liquid (203) mix at a specific temperature (or across avariety of temperatures), the headspace may be drawn off and analyzed bya previously calibrated gas analyzer. Based on the calculated amount ofmaterial in the gas and the temperature, the gas concentration may nowbe used to determine the concentration of the solute in the liquid (203)mix. For example, this technique could be used to measure theconcentration of ethanol in alcoholic beverages using only a traditionalbreath analyzer. This could be useful, for example, in a traffic stopwhere a law enforcement officer may suspect that a beverage containerincludes an alcoholic beverage, but requires some level of proof onsite.

While the inventions have been disclosed in connection with certainpreferred embodiments, this should not be taken as a limitation to allof the provided details of any invention. Modifications and variationsof the described embodiments may be made without departing from thespirit and scope of any invention herein disclosed, and otherembodiments should be understood to be encompassed in the presentdisclosure as would be understood by those of ordinary skill in the art.

The invention claimed is:
 1. A system for generating a vapor, the systemcomprising: a vessel having a thermally conductive foam placed therein;a liquid mixture of a solvent and a solute in said vessel so as to atleast partially submerge said foam in said liquid; means for heatingsaid foam to generate a vapor from said liquid, said vapor alsoincluding said solvent and said solute and said vapor and said liquidbeing in equilibrium.
 2. The system of claim 1 wherein said thermallyconductive foam is a metal foam.
 3. The system of claim 1 wherein saidsolvent is water and said solute is ethanol.
 4. The system of claim 1further comprising: means for detecting a temperature of said liquidmixture.
 5. The system of claim 4 wherein said means for detecting saidtemperature is external said vessel.
 6. The system of claim 4 whereinsaid means for detecting said temperature is internal said vessel.